I would do a couple of steps:
Download and install the current
macOS combo updater.
Rebuild the spotlight database.
After disabling, or uninstalling the Eset antivirus, Launch your Photos app.
Let it sit idle for some period of time. The Spotlight database, in my experience, can take an hour or two to rebuild. I have no idea how long it might take for the Photos library to be fully optimized, but I don't think it would be completely out of whack to take 4 or 5 hours for only 20,000 pictures.
Do an NVRAM reset.
If all that doesn't help in any significant way - I would boot to a macOS installer, and reinstall the system. Won't hurt anything, and might help in some way. (Who knows? You might have had some kind of wierdness creep into your system when you migrated from your old system.) A macOS reinstall should then act as a sort of repair install of the system. Has worked for that a couple of times in the past few years - but then I "mistreat" my system with a frequent install/uninstall for testing a variety of software, and it acts a little petulant for me occasionally. A reinstall is just my method of getting my system back in control.
)
If you must have an antivirus running on your system, wait until after you do whatever other system maintenance you might do, before your re-enable your AV.